1. Field of the Invention
This invention relates to a method of activating a silver halide photographic developer using a metal salt as a developing agent.
2. Description of the Prior Art
Commonly used developers for silver halide photographic light-sensitive materials are an aqueous alkaline solution of an organic compound such as a 3-pyrazolidone, a p-aminophenol derivative, a p-phenylenediamine derivative or hydroquinone as a developing agent, and, as is well known from the literature, an inorganic metal having a reducing property for exposed silver halide grains can be used as a developing agent but, in practice, is seldom used.
The reason for the non-use of such inorganic metals is that an organic developing agent as described above reduces a silver salt during developing and, thereafter changes into a relatively stable oxidation product which has no influence upon the reaction system, whereby the reduction potential of the developer remains stable and at a sufficiently active level, while an inorganic metal developing agent changes during development or during storage into a high valency metal which tends to change reversibly into a low valency metal, whereby the oxidation-reduction potential of the developer changes with an increase in the amount of materials developed, and cannot be kept at an active level.
Therefore, in order to maintain a stable active level using an inorganic metal as a developing agent, development must be carried out while electrolytically reducing the high valency metal formed in the developing reaction or uneconomical procedures must be taken such as using a large quantity of supplemental developing solution or throwing away the developer after use. However, such inorganic metal developing agents do have advantages in that they can be used in an acidic or neutral solution and the concentration of the developing agent can be raised, so it is very important to establish an economical method for using such solutions.